The present invention relates to control of the input drive level to traveling wave tube (TWT) amplifiers, and more particularly to improved techniques for optimizing TWT efficiency over a range of operating frequencies.
TWT amplifiers are in wide use in a variety of applications in which amplification of RF energy is required. Limitations imposed by TWT characteristics and manufacturing techniques result in a frequency-dependent input RF drive characteristic. These limitations can result in significant variations even between tubes of the same manufacturer and within the same manufacturing sequence. An optimum drive level for a given frequency will yield a maximum RF output power. Beyond that optimum drive level, defocusing and marked reduction of beam current transmission and TWT efficiency occurs. This results in increased power dissipation in the TWT RF structure and a decreased RF output power.
Insofar as applicants are aware, in the past, fixed, frequency dependent RF attenuators or gain equalizers tuned for each TWT amplifier have been employed to provide the optimum input RF drive level to the TWT. An alternative is to provide means for flattening the TWT amplifier gain and RF input driver characteristics for the frequencies used. Both alternatives are relatively expensive and are affected by the performance degradation of the amplifier during its operating life.
It would therefore be an advance in the art to provide an automated system for optimizing the RF drive level to a TWT amplifier, which provides an optimum RF drive for each frequency of concern, and allows for recalibration of the optimum RF drive as desired to compensate for aging of the TWT amplifier or other microwave chain components.